1. Field of the Invention
The present invention generally relates to a circuit board and a brushless DC motor using the circuit board, and more particularly, the present invention relates to a circuit board used by a brushless DC motor which includes a rotation control portion for controlling the rotation of the motor based on the data stored in a memory, and the brushless DC motor using the circuit board.
2. Description of the Related Art
Brushless DC motors are used for various applications such as office electronics, home electronics, and car electronics. In some applications, the rotation of such brushless DC motors needs to be controlled with great accuracy.
The rotation control portion of the brushless DC motor may be equipped with an IC having an integrated micro-computer. Generally, the micro-computers have embedded memories, and the micro-computer used for the rotation control portion includes a control program which regulates the driving current supplied to a stator based on a rotational state of the motor, temperature, and external signals. The rotation control of the motor including such a rotation control portion is usually more sophisticated compared to motors without such control portions.
Conventionally, a read only non-volatile memory (ROM) is used for the embedded memory of the micro-computer. The control program such as a feedback control program is written to the ROM of the micro-computer, and then the micro-computer is mounted on a circuit board. The circuit board is installed onto the brushless DC motor.
The rotational setting of such a brushless DC motor can be variously modified by modifying the control program written to the ROM. Even in the case that the required specification of the brushless DC motor is changed after the circuit board is already assembled, the rotational setting of the product may be modified by changing the data stored thereon. Therefore, it may not be necessary to prepare a new circuit board.
Generally, two kinds of memories are used for the embedded memories of the micro-computers; a one time programmable read only memory (an OTP-ROM) and an electrically erasable programmable ROM (an EEP-ROM or a flash memory). The OTP-ROM is inexpensive compared to the EEP-ROM or the flash memory. The ICs with the OTP-ROMs are usually purchased in the state that programs or data are already installed by chip suppliers. After writing the programs or data, the chip suppliers need to print some letters and numbers on the top of the IC to identify the program written thereto. In other words, the chip suppliers firstly write the data to the ICs, secondly verify the data written to the ICs, thirdly print letters and/or numbers thereon, and then ship the ICs to their customers. A batch of these processes should be separately performed for every program written to the ICs. Therefore, manufacturing of various kinds of the ICs with OTP-ROM, having different programs thereon, may take more time and the manufacturing cost for such ICs may be increased. In fact, the labeled price of the programmed ICs is about 20% to 50% higher, depending on the volume of the order, than that of a blank IC.
Therefore, in the case that various kinds of ICs are manufactured for circuit boards in small amounts, of which each includes a different control program, the manufacturing cost of the circuit boards is increased and the lead time thereof becomes longer.
In addition, the control program may not be quickly replaced in order to adapt the design and/or the rotational configuration changes of the motor. In order to replace the control program, first, a new control program is provided to the chip suppliers. Second, the chip supplier detaches the ICs with an old control program from a reel and rewrites the new program to the ICs. Third, new reference numbers and/or letters are printed on the IC. Therefore, the control program installed to the IC may not be quickly replaced. Moreover, the circuit board having the IC with the old control program is discarded or stored until it is reused, which creates an extra cost of manufacturing the circuit board.
The above problems may be overcome by purchasing blank ICs from the chip supplier and writing the control program to the IC with a ROM writer, for example. Generally, electric components including ICs are shipped in a Tape and Reel package, in which a plurality of electric components are taped in line in an equally spaced manner and are mounted on a reel. The Tape and Reel package is suitable for an automatic electric component mounting system. However, the control program needs to be written to the IC before the IC is mounted on the circuit board, and each IC needs to be detached from the Tape and Reel package to write the control program by using an ordinary ROM writer. Therefore, the automatic electric component mounting system cannot be used. Then, each IC is mounted to the circuit board by hand, which decreases the efficiency of the manufacturing process.